We can't run your code because of missing variables. I'd bet you're trying to delete something that doesn't exist, but don't really care. The easy way is to just wrap the line in try catch and ignore errors
try
delete(ball1);delete(ball2);delete(framex);delete(framey);
catch
end
Or you could use exist('ball1', 'var') to check for it in advance before deleting it.
if exist('ball1', 'var')
delete('ball1');
end
Finally, you could try
drawnow;
to make sure that the graphics are actually drawn and exist before deleting.
